Nematic liquid crystal composition and liquid crystal display element using same

Abstract

The present invention relates to a nematic liquid crystal composition containing a polymerizable compound and having a negative dielectric anisotropy (Δε) and PSA or PSVA liquid crystal display element produced by using the same. The liquid crystal composition according to the present invention can provide PSA or PSVA liquid crystal display element, in which a sufficient pretilt angle is included, the amount of remaining monomer is small, there are no or almost no problems, e.g., alignment defects and display defects, arisen from a low voltage holding rate (VHR) and the like, and excellent response performance is exhibited. A liquid crystal display element using the liquid crystal composition according to the present invention is useful for an active-matrix-drive liquid crystal display element and can be applied to PSA, PSVA, and other liquid crystal display elements.

Description

TECHNICAL FIELD[0001]The present invention relates to a liquid crystal composition containing a polymerizable compound and a liquid crystal display element using the same.BACKGROUND ART[0002]PSA (polymer sustained alignment) liquid crystal display devices have a structure in which a polymer structure is disposed in a cell so as to control the pretilt angle of liquid crystal molecules and have been developed as liquid crystal display elements because of rapid response and high contrast.[0003]The PSA liquid crystal display element is produced by injecting a polymerizable composition, which is composed of a liquid crystal compound and a polymerizable compound, between substrates and polymerizing the polymerizable compound while a voltage is applied and liquid crystal molecules are aligned so as to immobilize the alignment of the liquid crystal molecules. Known causes of image-sticking, which is a display defect of PSA liquid crystal display element, are impurities and a change in align...

AI Technical Summary

Benefits of technology

The composition achieves a high voltage holding rate, rapid response, and reduced alignment defects, ensuring excellent display quality and improved production efficiency by controlling the pretilt angle and minimizing residual monomers.

Problems solved by technology

Known causes of image-sticking, which is a display defect of PSA liquid crystal display element, are impurities and a change in alignment of liquid crystal molecules (change in pretilt angle).

For example, if a large amount of polymerization initiator is added such that the polymerization proceeds completely, the voltage holding rate of a display element is reduced because of remaining polymerization initiator, and the display quality is adversely affected.

Also, if the amount of polymerization initiator used at the time of polymerization is reduced in order to suppress reduction in the voltage holding rate, the polymerizable compound remains because the polymerization does not completely proceed, and an occurrence of image-sticking due to the remaining polymerizable compound is unavoidable.

However, in this case, upsizing of a production apparatus and reduction in the production efficiency are caused and, in addition, degradation of a liquid crystal material due to ultraviolet rays and the like occur.

Therefore, regarding the liquid crystal composition containing a polymerizable compound in the related art, it is difficult to reduce the amount of remaining of both uncured polymerizable compound and polymerization initiator at the same time.

That is, the cause of image-sticking is a change in the pretilt angle when the display element continues to display the same pattern for a long time because of differences in cured materials of the polymerizable compound.

However, these polymerizable compounds have low compatibility with liquid crystal compounds and precipitation of the polymerizable compounds occurs when liquid crystal compositions are prepared.

Therefore, it is difficult to apply these polymerizable compounds to practical liquid crystal compositions.

However, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate have no ring structure in the molecule and, therefore, there is a problem that sufficient alignment stability is not obtained because the affinity for liquid crystal compounds is weak and a force for regulating alignment is weak.

Consequently, it is difficult to sufficiently provide the characteristics, e.g., image-sticking characteristics of the display element, the alignment stability, the stability of the composition in which precipitation does not occur, and the production efficiency when PSA liquid crystal display element is produced, required of the liquid crystal composition containing a polymerizable compound.

Meanwhile, some components of the liquid crystal composition constituting the PSA display element are not suitable for use in the PSA display element.

However, there is a new problem related to alignment control, that is, after polymerization of the polymerizable compound, which is a production process of the PSA display element, provision of a pretilt angle to the liquid crystal molecules is hindered.

In the case where an appropriate pretilt angle is not provided to the liquid crystal molecules, the movement direction of the liquid crystal molecules at the time of driving cannot be regulated and problems occur, for example, liquid crystal molecules do not fall in the predetermined direction so as to degrade the contrast, and the response speed is decreased.

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